1. Field of the Invention
The invention relates to an inductively coupled power transfer (ICPT) system and a contactless ICPT device.
2. Description of the Related Art
An inductively coupled power transfer (ICPT) system, due to the capability of contactless electric power transfer, may replace some conventional conductive power transfer systems so as to avoid connections. Since a requirement for electric power is not always constant, an output voltage of the ICPT system may be unstable as a result of surplus electric power when a load supplied thereby decreases. Therefore, a control system is needed to maintain the same output voltage under different load conditions.
As shown in FIG. 1, when capacitance of a resonant circuit in the ICPT system is changed, a variation tendency of the output voltage is a bell curve. The curves with different Q factors are also depicted in FIG. 1. A point at which the output voltage has a maximum value is where the resonant circuit is fully-tuned. When the fully-tuned point is adopted as a demarcation, an interval where the capacitance is decreased represents an under-tuned interval, and an interval where the capacitance is increased represents an over-tuned interval.
A conventional ICPT system is disclosed in U.S. Patent Application Publication No. 20070109708. Capacitance of the conventional ICPT system is adjustable, and by adjusting the capacitance, an output voltage thereof may be controlled.
However, the conventional ICPT system has the following deficiencies:
1. Only one proportional-integral controller (PI controller) is used, so that the output voltage may be only controlled to one of increasing along with the capacitance, and decreasing along with the capacitance. In order to maintain the output voltage at a preset value, only one of the under-tuned interval and the over-tuned interval may be adopted for operation.
2. In the meantime, an operational point of the ICPT system may not approach the fully-tuned state, since when approaching the fully-tuned state, the output voltage changes dramatically along with the capacitance, so that an issue of the capacitance to be adjusted diverging in one direction because of accidentally striding across different operational intervals may take place and results in failed adjustment.
3. Further, the conventional ICPT system may be unsuitable for a load which requires a high output voltage since the operational point may not approach the fully-tuned state.